Increasing demands for distillate fuels and the decreasing supplies of lighter, easy-to-process crude are forcing refineries to process heavier stocks. The major problems encountered during the processing of these types of stocks are the higher nitrogen and sulfur contents, which on burning produce nitrogen and sulfur oxides (NOx and SOx), and cause serious environmental hazards.
The US Environmental Protection Agency (EPA) introduced regulations in 2000 that required the reduction of sulfur content of domestic gasoline from a previous maximum of 350 parts per million (ppm) to 30 ppm, to be phased in between 2004 and 2006 for all large refineries [1]. The EPA also introduced S15 (Ultra-Low Sulfur Diesel Fuel—ULSD) regulations requiring the reduction of highway diesel fuel sulfur down to 15 ppm beginning in June 2006; similar regulations were enacted in Canada [2]. Regulations were also enacted that required off-road diesel, locomotive, and marine fuel sulfur levels capped at 500 ppm by June 2007, with off-road diesel subsequently being capped at 15 ppm in 2010; even tougher regulations were enacted in the European Union and Japan [2]. Legislation has also led to a decrease of nitrogen in gasoline and diesel fuels.
Hydrodenitrogenation and hydrodesulfurization using hydrotreating catalysts, e.g., NiMo/Al2O3 and CoMo/Al2O3, is the conventional process currently being employed in refineries worldwide to remove organic nitrogen/sulfur compounds from liquid fuels. This process normally requires high temperatures, high pressure, and hydrogen consumption. The cost of hydrogen consumption represents about half of the operating costs of a refinery. The challenge that this conventional process faces is the new regulations announced by the U.S. Environmental Protection Agency (EPA) requiring the reduction of sulfur levels down to 30 weight part per million (ppmw) in gasoline and 15 ppmw in diesel as mentioned above. The current hydrodesulfurization process is effective to remove only the “easy sulfur” compounds but not the refractory sulfur compounds present in the liquid fuels. As well, although there is no limitation on nitrogen compounds, they compete with sulfur compounds on the active sites of catalysts in the conventional process. Therefore, nitrogen compounds should be removed as much as possible.
Meeting and exceeding the fuel specifications presents a significant challenge to petroleum refiners, who want to achieve this at the lowest possible cost. As well, though hydrotreating processes on hydrodenitrogenation (HDN) and hydrodesulfurization (HDS) have been significantly improved, it is still difficult to use the existing hydrotreating technology to remove the nitrogen and sulfur compounds to less than 15 ppm. This is partially due to the fact that the remaining nitrogen and sulfur compounds in commercial fuels are multi-ring nitrogen and sulfur compounds which are relatively difficult to remove [5,6].
U.S. Pat. No. 5,231,063 issued to Fukumoto et al. discloses a composite adsorbent containing acid salts of m- or p-aromatic amino acid and an acid used for removing aldehydes, amines and ammonia from a gas stream. When a transition metal is incorporated into the adsorbent, hydrogen sulphide can also be removed from the gas.
U.S. Pat. No. 4,145,314 issued to Fung et al. discloses methods of making highly dispersed metal catalysts using Group VIII metals and elemental phosphorous.
U.S. Pat. No. 5,045,522 issued to Kidd discloses an adsorbent for removing hydrogen sulphide from a fluid stream. The adsorbent includes zinc titanate, alumina and silica and metals from Group VIII along with phosphor, tungsten and molybdenum.
United States Patent Publication No. 2004/0007506 to Song et al. discloses methods and materials for the desulfurization of hydrocarbon fuels using a variety of materials such as transition metal chlorides, activated nickel absorbents, zeolites and the like.
U.S. Pat. No. 5,174,919 issued to Cymbaluk et al. discloses sulfur absorbents for removing sulfur from fluid streams. The absorbents include zinc oxide and a metal phosphate which may be from any of the following groups, Group IIA, Group IVB, Group IIIA and Group III.
United States Patent Publication No. 2006/0040823 to Stockwell discloses a catalytic additive for removal of NOx and SOx which includes an alkaline earth metal, phosphorous and a transition metal loaded on an alumina support.
U.S. Pat. Nos. 5,177,050 and 5,360,468 issued to Schubert discloses a sulfur absorbent composition which contains zinc oxide and alumina which is treated with a phosphating agent.
U.S. Pat. Nos. 5,039,644 and 5,124,302 issued to Lachman et al. disclose a monolithic ceramic structure used for supporting catalysts. The composition of the monolith includes alumina, titania, and/or zirconia and phosphate for stabilizing the metal oxide structure against thermal degredation during use as a catalyst support at high temperatures.
U.S. Pat. No. 3,904,550 issued to Pine discloses a hydrocarbon conversion catalyst support which includes alumina and aluminum phosphate.
U.S. Pat. No. 4,762,814 issued to Parrott et al. discloses a hydrocarbon conversion catalyst which includes alumina, zinc titanate, a molybdenum compound, a nickel or cobalt or both, and a compound containing phosphorous and oxygen. The catalyst is used for cleaning hydrocarbons to specifically remove compounds of nickel, vanadium and sulfur.
U.S. Pat. No. 6,471,923 issued to Becue et al. discloses materials for adsorbing and desorbing oxides of nitrogen (NO and NO2) present in exhaust gases produced for example by internal combustion engines. The materials contain phosphate tetrahedral containing and element from Groups IVB, VB, VIIB, VIIB and IVA. Other elements may be included from the alkali elements, alkaline earth elements and transition metals.
U.S. Pat. No. 4,251,350 issued to Johnson et al. discloses a hydrocarbon catalyst containing alumina, a Group VIB or VIII metal, a phosphorous containing compound which is mixed with hydrous alumina and calcined during the process of making the catalyst.
U.S. Pat. Nos. 4,588,706 and 4,648,963 issued to Kutes et al. discloses a hydrocarbon catalyst for removing sulfur and nitrogen from hydrocarbons. The catalyst is made by mixing a metal oxide with the metal being from the Group VIB, with a Group VIII metal which is either iron, cobalt or nickel, and with phosphoric acid and then mixing the material with a alumina support material and then heating the mixture to dry it then heating in a non oxidizing and non reducing environment to activate the mixture.
U.S. Pat. No. 5,135,902 issued to Delaney et al. discloses a catalyst containing nickel, tungsten and phosphorous supported on a porous refractory oxide. The catalyst is designed to promote an aromatic saturation reaction.
U.S. Pat. No. 4,853,108 issued to Kemp discloses a catalyst containing incorporating elements selected from the group consisting of molybdenum, tungsten and mixtures thereof, and a stabilizing amount of phosphorus into an alumina hydrogel support.
Therefore there is a strong need for adsorbent materials that can selectively adsorb organonitrogen and organosulfur from transportation fuels at room temperature and atmospheric pressure, which does not require the presence of hydrogen if possible.